FIGURE 7: Output ripple of Q25D15/24 on -Vout as
shown in Figure 4.
FIGURE 8: Output ripple of Q25D15/24 on -Vout with another external
cap of Nippon Chemi-Con 180µF@16V on
the -Vout. The part number is 16PS180MH11.
Multiple Q25 converters can be synchronized together simply
The SYNC pin can be used to synchronize the internal os- by connecting the converters SYNC pins together as shown in figure
cilllator to external clock. An open drain output is the recommended 8. Care should be taken to ensure the ground potential differences
interface between the external clock to the Q25 SYNC pin as shown between the converters are minimized. In this configuration all the
in figure 7. The clock pulse width must be greater than 15ns. The converters will be synchronized to the highest frequeny device. The
external clock frequency must be greater than the frequency of the SYNC pin is a CMOS buffer with pull-up current limited to 200micro
amps. If the external device forces the SYNC pin low before the
internal oscillator ramp completes its charging cycle, the ramp will
reset and another cycle begins. If the SYNC pins of multiple Q25
converters are connected together, the first SYNC pin that pulls low
will reset the oscillator ramp of all the other converters. All converters
will operate in phase when synchronized using the SYNC feature.
Up to five devices can be synchronized using this method.
FIGURE 9. SYNC from external clock
FIGURE 10. SYNC of multiple devices
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